If your servo is grinding , you probably have a stripped gear. You can find top of the line/ heavy duty servo, used, on this forum , cheap.
One important thing to remember is that you esc is programmable, it will be noticeably slow if it's on wrong setting!!!!!!!!!
Radio MUST be set up to the esc!!!! or it can make your car slow.
Are you running stock or mod? Comm cut and brushes are a must occasionally for racing.
How old are your batteries? Old batteries will be very slow as the new 3800 are running oner 1.2V, which 3300 could not do.
If tires are worn out you will be slower.
Check all of the above on your car carefully.